using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            int Num = 1;
            int InputNum = 0;

            string[] str = Console.ReadLine().Split(' ');

            for (int i = 1; i<=9 ; i++)
            {
                InputNum = Convert.ToInt32(str[i]);
                if ( InputNum == Num )
                {
                    Num++;
                }
                else
                {
                    Console.WriteLine(Num);
                    break;
                }                  
            }   
        }
    }
}